Use --sysroot when compiling against the NDK

Match the NDK build by using --sysroot to point to the NDK headers
rather than manually specifying the include directories with -isystem.
Also remove --nostdlibinc from the global cflags so it is not used
for NDK builds, and manually add it back for non-NDK builds.

This relands I20d5605a3154bf51d64132ac1d8ea427eda32066 with a fix
to also apply -nostdlibinc to vendor modules defined in Android.mk
files.

Bug: 374130155
Test: builds
Flag: EXEMPT refactor
Change-Id: I90bedfe00d4fd1f4d94f562e5fe65da55ae16e07